Hand-held rotary tools are widely used by many people, including drywallers, professional remodelers, tile installers, homeowners, and artists. These rotary tools typically include an outer housing designed to be easily held within a human hand. The housing retains an electric motor which is operable to drive a rotatable collet or chuck of the rotary tool. An accessory may be releasably coupled with the collet thereby enabling the rotary tool to rotatably drive the accessory.
The widespread use of hand-held rotary tools is a result, in part, of the wide variety of accessories that may be used with the tools. The accessories include various cutting bits, cut-off wheels, polishing wheels, grinding wheels, and sanding discs. Another accessory is a device used to form larger holes in a material. This accessory is referred to as a “hole saw.”
Some conventional hole saws share design features that prohibit such saws from being capable of removing chips from the cutting site in an efficient manner. The major design features that cause this inefficiency appear to include the number of teeth, the side clearance, and the absence of a chip conveyance device. When the teeth in these devices become filled with debris, the cutting process slows dramatically due to energy wasted to compact or churn the wood chips.
For example, some prior art hole saws have either a four or six teeth per inch (tpi) configuration which causes small gullets, or the open area adjacent to the cutting edge of the teeth, to have quite a small cross-sectional area. These small “primary” gullets can be easily clogged by chips during the cutting process which prevents each tooth from cutting effectively.
The lack of an efficient means for removing debris is compounded by the practice in many known hole saws of using an alternating set pattern on the teeth. An “alternating set” is a pattern wherein one tooth is configured to cut along an arc with a diameter larger than the diameter of the body of the saw while an adjacent tooth cuts along an arc with a diameter smaller than the diameter of the body of the saw. The alternating set thus provides the necessary clearance for the outside diameter (“OD”) and inside diameter (“ID”) of the saw body. The generation of a cut line that is wider than the nominal width of the saw is acceptable when the tooth exits the cutting media, as in the case of circular saws, since the excess material is easily removed from the area whereat material is being removed by the saw. In the case of a hole saw, however, the excess material simply adds to the problem of clogging.
One hole saw which overcomes some of the problems identified above is disclosed in U.S. Pat. No. 5,803,677 of Brutscher, et al. which issued on Sep. 8, 1998. The device disclosed in U.S. Pat. No. 5,803,677 includes a cup with two cutting teeth positioned on the open end of the cup. The two cutting teeth are substantially diametrically opposed to one another to provide a balanced cutting engagement of the media and are spaced apart by a chord length of between about 45 to about 180 degrees. A pair of secondary gullets are positioned in the cup proximate to a forward cutting edge of the two cutting teeth. The secondary gullets have a predetermined depth and shape along a longitudinal axis of the cup to suitably remove debris from the cup during a portion of the duration of the hole cut. A plurality of raker teeth may be positioned on the chords defining the spacing between the cutting teeth. The raker teeth are disposed below the cutting teeth, approximately 0.030 inches to engage and move cutting debris formed by the cutting teeth. Accordingly, the device disclosed in U.S. Pat. No. 5,803,677 provides for improved removal of debris.
What is needed is a configuration for a hole saw that provides increased speed.